1. Field of the Invention
This invention relates generally to a protocol adapter for passing diagnostic messages between networks within a vehicle and a host computer and, more particularly, to a protocol adapter for passing diagnostic messages between networks within a vehicle and a host computer, where the protocol adapter includes a pass-through mode of operation where the protocol adapter emulates legacy protocol adapters so that state of the art host computers can communicate with the vehicle networks using obsolete software.
2. Discussion of the Related Art
Vehicles employ various networks and systems for diagnostics, analysis and monitoring of vehicle systems. These various networks are generally selectively connectable to an external host computer so that the operation of the vehicle networks can be monitored by an external system. These vehicle systems and networks operate under various protocols, such as the J1708 and the J1939 protocols. Protocol adapters are known in the art that allow the host computer to communicate with the vehicle networks through the protocols.
One known type of protocol adapter for this purpose is the J1708 protocol adapter. The first generation of the J1708 protocol adapter used for diagnostic purposes included a voltage translator with a built-in-timer circuit that flagged the end of a message. This protocol adapter design worked well for J1708 protocols because it and the standard serial communication port of the host computer were based on universal asynchronous receive and transmit (UART) technology having different physical interfaces, i.e., different voltages. The timer circuit was needed to allow the host computer to recognize the end of message as defined by the J1708 protocol. Most host computers, however, did not have adequate resources to comply with the rigid timing requirements needed for end of message detection.
A second generation protocol for vehicle diagnostics purposes is the J1939 protocol. With the J1939 protocol, there was no longer a basic compatibility between the known host computer serial communication port and the J1939 protocol. It therefore became necessary for protocol adapters to use microprocessors in their diagnostic tools. These microprocessors would receive an entire message from one of the supported links, and do message validation, including end of message detection. The microprocessor would then forward the message on to the appropriate communication channel if it did not detect an error. This alleviated the need for the timer to detect the end of message, but also added an inherent delay between the vehicle data link and the host computer serial communication port.
The J1939 protocol required that software had to be matched to the diagnostic tool for which it was written. Obsolete software had to be paired with legacy hardware, and new software had to be paired with new hardware. This required that each diagnostic shop own and maintain several diagnostic tools. It would be desirable to have a protocol adapter that could operate as an old voltage translator to support obsolete software using the J1708 protocol, and recognize when the protocol adapter is connected to a host computer running new software to automatically switch to the J1939 protocol.